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1-134 SOMobjects Base Toolkit: Programmer’s Reference Manual

somDispatch, somClassDispatch Methods

Purpose

Invokes a method using dispatch method resolution. The somDispatch method is designed

to be overridden. The somClassDispatch method is not generally overridden.

IDL Syntax

boolean somDispatch (

out somToken retValue,

in somId methodId,

in va_list args);

boolean somClassDispatch (

in SOMClass clsObj,

out somToken retValue,

in somId methodId,

in va_list args);

Note: For backward compatibility, these methods do not take an Environment parameter.

Description

Both somDispatch and somClassDispatch perform method resolution to select a method

procedure, and then invoke this procedure on args. The “somSelf” argument for the

selected method procedure (called the “target object,” in the following text, to distinguish it

from the receiver of the somDispatch or somClassDispatch method call) is the first

argument included in the va_list, args.

For somDispatch, method resolution is performed using the class of the receiver; for

somClassDispatch, method resolution is performed using the argument class, clsObj.

Because somClassDispatch uses clsObj for method resolution, a programmer invoking

somDispatch or somClassDispatch should assure that the class of the target object is

either derived from or is identical to the class used for method resolution; otherwise, a

run-time error will likely result when the target object is passed to the resolved procedure.

Although not necessary, the receiver is usually also the target object.

The somDispatch and somClassDispatch methods supersede the somDispatchX

methods. Unlike the somDispatchX methods, which are restricted to few return types, the

somDispatch and somClassDispatch methods make no assumptions concerning the

result returned by the method to be invoked. Thus, somDispatch and somClassDispatch

can be used to invoke methods that return structures. The somDispatchX methods now

invoke somDispatch, so overriding somDispatch serves to override the somDispatchX

methods as well.

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Bull DPX/20 Betriebsanweisung Seite 146